There has been known a method of manufacturing a semiconductor device where a glass layer for passivation is formed such that the glass layer covers a pn junction exposure portion in a process of manufacturing a mesa semiconductor device (see patent document 1, for example).
FIG. 12(a) to FIG. 12(d) and FIG. 13(a) to FIG. 13(d) are views for explaining such a conventional method of manufacturing a semiconductor device. FIG. 12(a) to FIG. 12(d) and FIG. 13(a) to FIG. 13(d) are views showing respective steps.
The conventional method of manufacturing a semiconductor device includes, as shown in FIG. 12 and FIG. 13, “semiconductor base body forming step”, “trench forming step”, “glass layer forming step”, “photoresist forming step”, “oxide film removing step”, “roughened surface region forming step”, “electrode forming step”, and “semiconductor base body cutting step” in this order. Hereinafter, the conventional method of manufacturing a semiconductor device is explained in order of steps.
(a) Semiconductor Base Body Forming Step
Firstly, a p+ type diffusion layer 912 is formed by diffusion of a p type impurity from one surface of an n− type semiconductor substrate (n− type silicon substrate) 910, and an n+ type diffusion layer 914 is formed by diffusion of an n type impurity from the other surface of the n− type semiconductor substrate 910 thus forming a semiconductor base body in which a pn junction arranged parallel to a main surface of the semiconductor base body is formed. Thereafter, oxide films 916, 918 are formed by thermal oxidation on a surface of the p+ type diffusion layer 912 and a surface of the n+ type diffusion layer 914 respectively (see FIG. 12(a)).
(b) Trench Forming Step
Next, a predetermined opening portion is formed on the oxide film 916 at a predetermined position by photo etching. After etching the oxide film, subsequently, the semiconductor base body is etched thus forming a trench 920 having a depth exceeding the pn junction from one surface of the semiconductor base body (see FIG. 12(b)).
(c) Glass Layer Forming Step
Next, a layer made of glass composition for protecting a semiconductor junction is formed on an inner surface of the trench 920 and a surface of the semiconductor base body in the vicinity of the trench 920 by an electrophoresis method, and the layer made of glass composition for protecting a semiconductor junction is baked so that a glass layer 924 for passivation is formed on a surface of the trench 920 (see FIG. 12(c)).
(d) Photoresist Forming Step
Next, a photoresist 926 is formed such that the photoresist 926 covers a surface of the glass layer 924 (see FIG. 12(d)).
(e) Oxide Film Removing Step
Next, the oxide film 916 is etched using the photoresist 926 as a mask so that the oxide film 916 at a portion 930 where a Ni-plating electrode film is to be formed is removed (see FIG. 13(a)).
(f) Roughened Surface Region Forming Step
Next, a surface of the semiconductor base body at the portion 930 where a Ni-plating electrode film is to be formed is subjected to surface roughening treatment thus forming a roughened surface region 932 for enhancing adhesiveness between a Ni plating electrode and the semiconductor base body (see FIG. 13(b)).
(g) Electrode Forming Step
Next, a Ni plating is applied to the semiconductor base body thus forming an anode electrode 934 on the roughened surface region 932 and forming a cathode electrode 936 on the other surface of the semiconductor base body (see FIG. 13(c)). Annealing of the anode electrode 934 and the cathode electrode 936 is performed at a temperature of 600 degrees under a nitrogen atmosphere, for example.
(h) Semiconductor Base Body Cutting Step
Next, the semiconductor base body is cut by dicing or the like at a center portion of the glass layer 924 thus dividing the semiconductor base body into a plurality of chips whereby mesa semiconductor devices (pn diodes) are manufactured (see FIG. 13(d)).
As has been explained heretofore, the conventional method of manufacturing a semiconductor device includes the step of forming the trench 920 exceeding the pn junction on one surface of the semiconductor base body where the pn junction arranged parallel to the main surface is formed (see FIG. 12(a) and FIG. 12(b)), and the step of forming the glass layer 924 for passivation in the inside of the trench 920 such that the glass layer 924 covers a pn junction exposure portion (see FIG. 12(c)). Accordingly, in the conventional method of manufacturing a semiconductor device, by cutting the semiconductor base body after forming the glass layer 924 for passivation in the inside of the trench 920, mesa semiconductor devices having high breakdown strength (breakdown voltage) can be manufactured.